1. Field of the Invention
This invention relates to a steering assembly supporting construction for fitting a steering device of a motor vehicle to a body of the vehicle.
2. Description of a prior art
Generally, in a steering assembly supporting construction of a motor vehicle, a steering shaft which transmits turning force of a steering wheel to a gear box is supported rotatably within a steering column which is arranged in an upwardly inclined orientation, with upper and lower portions of the column fitted to a member on the car body (a dash panel, for example) via a bracket. (Refer to U.S. Pat. No. 4,362,319 and Japanese Utility Model Registration Application Laying Open Gazette No. 58-111668).
Various standards have been established for motor vehicles, one of which provides for the quantity or extent of movement of a steering wheel toward the rear of a driver's compartment upon the occurrence of a collision (hereinafter referred to as "extent of rearward movement of a steering wheel"). The extent of rearward movement of a steering wheel is generally regarded as corresponding to the distance of horizontal movement of a steering wheel toward the rear of a driver's compartment caused by rearward movement of auxiliary machine members, such as an engine, in an engine compartment at the front of a car body toward the driver's compartment upon the occurrence of a head-on collision, for example.
In order to suppress such extent of rearward movement of the steering wheel, it is known to provide a supporting member which connects a lower part of the steering column to a member on the car body in such a fashion that the connected state of the steering column can be released so as to move the steering wheel upwardly, upon the occurrence of a collision, by rotating the steering column around a supporting point whereat the steering column is supported by the car body (refer to Japanese Utility Model Registration Application Laying Open Gazette No. 62-117169).
However, the release of the connected state between the steering column and the supporting member is so composed that release is achieved by movement of the dash panel, which is a portion of the car body, toward the driver's compartment side upon the occurrence of a collision. The movement of the dash panel toward the driver's compartment upon the occurrence of a collision takes place at a relatively later stage of the collision. Therefore, the dash panel will in some cases move only after or as it is deformed in complicated manners. In such cases, the release of the steering column cannot be achieved as desired.
Upon rotation of the steering column, the steering wheel is moved upwardly. However, it is necessary to control the amount of upward movement of the steering wheel to improve safety during collision. In this connection, suppose a driver bumps his head against the steering wheel during the collision. It is desirable in an ordinary motor vehicle to increase the amount of upward movement of the steering wheel due to the rotation of the steering column so that the head of the driver strikes against a ring-shaped part of the steering wheel which is less rigid than a boss or central part of the steering wheel. On the other hand, in a motor vehicle having an airbag device, for example, at the boss or central part of the steering wheel, it is necessary to lessen the amount of upward movement of the steering wheel due to the rotation of the steering column. Control of the amount of upward movement of the steering wheel can be achieved by adjusting the timing of releasing the connected state of the steering column with the supporting member.